heater block temperature gradient

This weekend the Sock on my hotend died (became floppy and fell off). Since the nozzle needed cleaning I didn't replace it right away but carried on printing.

This Monday morning notice all parts printed showed more signs of ooze than usual + there was some stringing.

Hypothesis: without protection from the Sock, the fan (kickstarter original!) cools the left side of the heater block which is where the thermocouple is mounted. Marlin makes the heater cartridge work to maintain temperature. Net result is a left/right temperature gradient across the hotend and much of the filament experiences a temperature greater than that on the dial. Hence oozing.

The heater block shouldn't be subjected to airflow from a part cooling fan, if it is the duct needs adjusted/redesigned.

I modeled it once, assuming there isn't a fan blowing on the heater block the temperature gradient was less than 2degC throughout the block at printing temperatures. I included the ~7w of heat flow into the nozzle, as that's average for melting an average polymer at average flow rates. Then 5-7w goes up the heatbreak, and about 5w lost to ambient.